We will study synthesis and release of the hormone arginine vasopressin. Steady-state vasopressin mRNA levels will be measured by in situ hybridization techniques using sensitive and specific cDNA probes. Vasopressin release will be monitored by measuring the peptide by radioimmunoassay in culture medium. The first set of studies will focus on vasopressin mRNA dynamics in the suprachiasmatic nuclei (SCN), the site of a known circadian pacemaker. This will be investigated by (i) more precisely defining the time course of our newly discovered vasopressin mRNA rhythm in SCN, (ii) examining the hormonal specificity of this rhythm, and (iii) delineating the developmental onset of the mRNA rhythm. The second set of studies will focus on vasopressin release from SCN. This will be investigated by (i) further developing and validating our perifusion system for studying rhythmic vasopressin release from SCN explants in culture; (ii) examining the specificity of the release rhythm from SCN; and (iii) studying the role of membrane excitability in rhythmic vasopressin release. The third set of studies will focus on (i) probing the relationship between these endogenous rhythms of vasopressin synthesis (mRNA) and release, and (ii) using vasopressin release as a means to study actual circadian clock mechanisms. The results of these studies will provide new insights into mechanisms underlying synthesis and release of peptide hormones.